Characteristics,risk Assessment And Source Analysis Of Heavy Metal Pollution In Qingshan Lake,huangshi City

Qingshan Lake is located in the northeast of Huangshi City.It is the second largest urban lake in Huangshi City.It has functions such as regulating climate,preventing floods and droughts,maintaining ecological balance,and landscapes appreciation.Its environmental changes are closely related to human life in the region.In recent years,with the continuous development of industrialization and urbanization in Huangshi City,a large amount of pollutants have entered Qingshan Lake.Most of the heavy metals entering the lake are adsorbed by the sediment and accumulate continuously in the sediment.Since heavy metals are non-degradable and highly toxic to the human body,it will cause serious harm to the human and ecosystem.Government departments have adopted many methods to control Qingshan Lake.However,some studies have shown that the treatment effect of Qingshan Lake is not good,which may be caused by the endogenous release of heavy metals.Therefore,it is of great significance to study the distribution characteristics and ecological risk assessment of heavy metals in Qingshan Lake sediments,explore the historical process of heavy metal pollution and its correlation with sediments,and clarify the sources of heavy metals in Qingshan Lake sediments for the related treatment of heavy metals in Qingshan Lake sediments.In this paper,10 surface sediments and 1 columnar sediments of Qingshan Lake were collected,and the total amount,particle size,loss on ignition,and the content of each heavy metal in the surface sediments and cores of Qingshan Lake were analyzed.The contamination history of cores established with spherical carbon（SCP）and the contamination status and risk level of heavy metals in the study area were assessed.We use Grapher 9.0 to draw the spatial distribution,pollution and risk levels of heavy metals,and use Excel 2003 and SPSS 18.0 to perform correlation analysis and principal component analysis on heavy metal data to explore the sources of heavy metals.The main results are as follows:（1）The contents of heavy metal elements Cr,Pb,Ni,Cu and Zn in the surface sediments of Qingshan Lake were 34.88-69.88,68.41-102.29,38.76-51.10,99.91-479.43 and 217.83-384.98 mg/kg,respectively,with an average value of 59.17,82.48,46.26,201.16 and 300.18 mg/kg.From the perspective of spatial distribution,the spatial distribution characteristics of heavy metal elements Cu,Pb,Zn and Cr in the surface sediments of Qingshan Lake are relatively similar,with higher contents in the west and east and lower contents in the middle.The spatial distribution of Ni is different from that of other heavy metals,which is higher in the east and lower in the west.（2）Among the heavy metal elements in the surface sediments of Qingshan Lake,Zn is mainly in the reducible state,Cu and Pb are mainly in the oxidizable state,Ni and Cr are mainly in the residual state.In terms of bioavailable state,the order of bioavailable state content of each element is:Cu>Pb>Zn>Cr>Ni.（3）The results of the geo-accumulation index method showed that the pollution levels of heavy metals were in the following order:Cu>Zn>Pb>Ni>Cr.The results of the potential ecological risk index method showed that the potential risk of heavy metal elements was:Cu>Pb>Ni>Zn>Cr,and the comprehensive risk of all sample points was slight pollution.The results of the secondary/primary ratio method showed that Qingshan Lake was greatly affected by human activities,and the order of heavy metal risk was:Cu>Pb>Zn>Cr>Ni.（4）Spherical carbon dating shows that the average deposition rate of Qingshan Lake since 1995 was 1.25 cm·a^-1,the average deposition rate from 1950s to 1995 was0.5 cm·a^-1,and the deposition rate before 1950s was 0.3 cm·a^-1.The evolution of heavy metal content in Qingshan Lake can be divided into four stages:before the1950s,the industrial and agricultural output value in Huangshi region was low,the industrial level was relatively backward,and the degree of heavy metal pollution was low;from 1950s to 1980s,the industry developed,but the development speed was relatively slow,and the degree of heavy metal pollution was still low;1980s-2000s,heavy industry continued to develop,and a large number of heavy metal pollutants were discharged into the environment,and the content of heavy metals rose rapidly;since 2000s,mineral resources have been gradually depleted,and with the upgrading of industrial technology and the introduction of environmental protection regulations,heavy metal pollution has been controlled.（5）The correlation analysis results show that the sediment particle size in the columnar core has no significant effect on the content of heavy metal elements,while the magnetic susceptibility and organic matter have a significant effect on the content of heavy metal elements.Pb,Cu,Zn may have the same or similar sources.According to the principal component analysis and synthesis of the distribution and variation characteristics of heavy metal content,it can be known that the five heavy metals can be divided into two categories,Pb,Cu,Zn are the first category;Cr and Ni are the second category.After comprehensive analysis,it is determined that Cr and Ni mainly come from natural sources,and Pb,Cu and Zn mainly come from human activities.